However, this doesn’t make much sense. The ID is our primary key to the ‘country’ list. Why are we querying by value? I mean, if the United Kingdom had a revolution and suddenly became, say, the ‘United Republic’, all of my CAML queries would break.

Edit: One of my colleagues pointed out that in SharePoint 2010, if you update the text of a referenced item, it is updated within the items that reference it. This is different to SharePoint 2007, where the referencing items retained the original text value. He’s right – but I’d still prefer to query by ID as it’s indexed, unique, and simple.